Why Do Mushrooms Grow In Houseplants: Exploring the Root Cause

It can be a bit of a shock when mushrooms turn up in your houseplants. Due to their lifecycle, they can literally turn up overnight.

Mushrooms turning up in houseplants is a fairly neutral event most of the time. They won’t harm the plant, but they’re unlikely to be particularly beneficial either.

So how did the mushroom get there? In short, the spores ended up in your plant, and at some point the conditions were right and the spore germinated, mycelium grew, and a mushroom followed.

That is all that we can take away from the event.

It doesn’t indicate good soil or bad soil.

All that we know is that your houseplant soil has the right amount of moisture and nutrients to support a mushroom.

It has little bearing on the health of your plant, but if your plant is, e.g. a snake plant that likes to dry out a lot, it may be time to check the roots and soil and ensure it’s not staying too wet for too long.

This article is a deep-dive into why mushrooms grow in houseplants. If you want a run-through of what they are, where they came from, how toxic are, how to get rid of them, whether to get rid of them etc, read this article.

What species are houseplant mushrooms?

A houseplant mushroom isn’t just any mushroom.

By which I mean that it’s a specific species. I kind of made that sound like it was a magic mushroom. Or a mushroom with superpowers. Which it definitely isn’t.

Chances are the mushroom that just appeared in your potted plant is Leucocoprinus birnbaumii.

It could be another species of Leucocoprinus, such as a leucocoprinus cepistipes but an absolute identification doesn’t really matter. It’ll probably be a leucocoprinus of some description.

Some are poisonous, some aren’t, so don’t chance it.

There’s a lot of variation in leucocoprinus birnbaumii, depending on the conditions they’ve grown in. The ones that turn up in houseplant soil tend to be quite small, tall and thin because there’s only so much water and nutrients to go around, and they have to compete with your plant.

They probs look something like this:

They may not, and that’s okay. Feel free to dm me a picture on Instagram and we’ll see if we can identify it. Be quick though, because they often don’t last more than a couple of days.

Where do leucocoprinus birnbaumii come from?

Leucocoprinus birnbaumii used live exclusively in the tropics and the subtropics. They weren’t found in northern Europe because it’s too cold.

They’re small and yellow and can grow either singly or in a clump (I’ve had both in my plants).

They’re classified as medium toxic, so don’t eat them. If you do, you’ll likely get a very stomachache, but you’d need to eat a lot to do significant damage.

The mushroom is the fruit of the fungi, and just turns up when it’s ready (like…a fruit) but the mycelium (the fungal equivalent of a root system) can lie dormant for years. They tend to be pretty small but the cap can get up to 7.5 cm in diameter.

Whilst leucocoprinus birnbaumii tend to be bright yellow, they can vary in colour depending on their lifecycle and the nutrient breakdown of your soil. Houseplant mushrooms can be white, green, or brown.

Hilariously, they were first described (i.e. formally identified as a newly encountered species) in 1788 in Halifax. Yeah, where Last Tango In Halifax was set.

A good few thousand miles from where they’re supposed to be.

And then it turned up in London. And Prague. All of these are distinctly non-tropical places.

Due to this tendency to hitchhike around the world, leucocoprinus birnbaumii wasn’t correctly classified until 1962, when Rolf Singer reclassified leucocoprinus luteus as leucocoprinus birnbaumii.

At this point you might be thinking, ‘ why does the species of mushroom matter? I want to know why it grew in my plant.’

The species does matter because leucocoprinus birnbaumii is very, very good at spreading via potting soil.

It travelled from the tropics to Europe in our houseplants. It turned up a lot in greenhouses and hothouses but likely wasn’t an issue for the general public until central heating became commonplace.

In short, houseplant mushrooms are a direct result of the houseplant industry. They came over in imported plants, their mycelium likely attached to the roots of the tropical plants destined for the trade, and occasionally pop up, freaking out everyone.

There are now Leucocoprinus birnbaumii living wild in the forests of England. It was like they planned it all along.

Due to the long and varied history of trying to classify Leucocoprinus birnbaumii, they can be given a variety of names.

Alternative names for leucocoprinus birnbaumii

• Plantpot dapperling
• yellow parasol
• flowerpot parasol
• yellow houseplant mushroom (fair enough)
• lemon yellow lepiota
• yellow pleated parasol
• lepiota lutea

Where did the mushrooms in my house plant come from?

Houseplant soil from the growers

The most likely explanation is that the spores were there all the time, and have been since your plant was first potted up in soil and grown on in a commercial nursery.

Mushrooms produce billions of spores, which they eject out of their gills. The spores and then carried by the wind (or, in our case, by us) and spread that way.

The reason this particular species of mushroom frequently turns up in houseplant soil is that the potting mix is suitable for it. It’s a tropical fungi, and the potting mix is designed for a tropical plant.

The spores are so tiny my brain can’t really comprehend them, but a single button mushroom can produce more than 3 billion spores. So one tiny mushroom in a commercial greenhouse could easily get spores into every pot. And we can probably imagine there’s more than one – a greenhouse is the perfect place for leucocoprinus birnbaumii to grow and reproduce.

Growers could eradicate them, but houseplant mushrooms are saprotrophic, which means they feed on decaying matter in the soil and won’t cause harm to the plants – they could actually potentially benefit their root system.

Bagged potting soil can also come with added mushrooms, but I would treat this as a good thing. The presence of fungi suggests that the soil hasn’t been treated with fungicides or pesticides, and a dark, warm bag of soil is the perfect place for them.

They can be a sign that the soil is nutrient-rich – this, like the mushrooms themselves, is not an automatic indicator of ‘good’ soil. Nutrients are a component of good soil, but they’re not the whole picture.

They could have come in on you

If you're near a mushroom that's releasing spores in a garden centre (I honestly have no idea how likely that is) they could get caught on your clothes, and then fall into a houseplant. 

These things can travel from Malaysia to Prague, I'm sure a trip from your sleeve to the soil is nothing to it.

Just think – if your cat was near a mushroom releasing its spores, got some on its fur, and then went for a kip in your Monstera, it wouldn’t take much for a spore to set up shop in the soil.

How do houseplant mushrooms pop up overnight?

If it seems like your houseplant mushroom was gone one minute and fully formed the next, it’s because they spend a long time forming and then appear one day, looking like they’ve been there for weeks.

And then, a couple of days later, there’s no sign that they’ve been there at all.

As I said before, the mushroom is the fruit. It popped up, spread its spores, and then shrivelled up, and then more or less reabsorbed itself.

The real power behind the mushroom is the mycelium, which is a network of fungal threads called hyphae that act like a root system, absorbing water and nutrients.

Fungi can’t photosynthesis because they don’t have chlorophyll.

They have other ways of getting food, but they often enter a symbiotic relationship with plants. 

They attach their mycelium to the roots of the plant. The plant can use the mycelium as an extension of its root system, and the mycelium can absorb carbohydrates from the plant.

And you might be thinking ‘…wait, if my houseplant’s pet mushroom just released a few million spores around my house, why aren’t there mushrooms popping up in all my plants?‘

Good question. Because it only takes a single spore to start a mycelium

Why are there mushrooms growing in my houseplant?

Short answer: the conditions were right.

What conditions do houseplant mushrooms need?

I’ll briefly run through them, but remember that mushrooms can just turn up. Whilst they’re more likely to turn up in certain conditions, these are guidelines, not rules. A bit like how spider mites love the dry, bright places, but will turn up on Calathea in December.

Light

The natural habitat of leucocoprinus birnbaumii is on the first floor, usually in leaf litter, or perhaps near a rotten tree. It’s usually pretty shady around there, but there might be dappled light.

Mushrooms are more likely to turn up in shaded areas, but they can grow in bright light.

Also, plants in bright light could provide shade for the mushroom, so whilst the plant is in bright light, the mushroom isn’t.

Humidity

Leucocoprinus birnbaumii will likely only produce mushrooms when they’re in a humid environment, so if your home has very dry air, you might never see one. The spores need humidity to germinate, so they’re less likely to grow in cacti, but they could germinate in a peace lily.

Once the spore has germinated, the mycelium will start to grow, but the mushrooms won't grow unless the right conditions are met. 

That could be next week, or in 10 years. 

The soil could be moist enough for the spore to germinate (if it's deep enough in the soil) but if the top few inches of the soil regularly dries out, you'll likely never get mushrooms appearing.

Temperature

Spores need quite warm temperatures to germinate, so the fruit won’t develop until it’s warm enough, otherwise, it’s a waste of a couple of billion spores.

So if your environment rarely gets warm and humid, you won’t get mushrooms in your houseplants.

Again, I’ve had them pop in my chilly bathroom, so they sometimes manage to find a way.

Water

Mushrooms like growing in damp soil. They are highly unlikely to grow if the soil isn’t wet.

Whilst having mushrooms growing in your houseplants isn't necessarily a sign that you're overwatering your plants - it's always be worth checking the roots, just in case.

Some plants are more prone to mushrooms than others, simply due to the conditions they’re typically kept in or prefer.

Pothos get them quite often, because they’re often kept in low light levels, so the soil doesn’t evaporate very quickly and stays moist for longer. Dark + moisture = mushrooms.

In general, I wouldn’t worry about mushrooms in your houseplants if the species of plants getting them are also from damp places in the tropics, like rainforests.

So Calathea, ferns, Aglaonema some Philodendron, bird of paradise, spider plants, Monstera, some Anthurium… there’s probably more.

However, there are some species of plant that like to dry out quickly and shouldn’t really be in soil staying damp enough to grow a mushroom.

Plants like snake plants, succulents, and cacti.

If, for example, your snake plant does have a mushroom, it's not necessarily got root rot, but check just in case. 

It could have a layer of compost, or some other nutrient-rich humus on top that provided decent conditions for your mushroom, but the substrate below was free-draining. 

They can also occur on big succulents, because when leaves drop (from old age or whatever) they slowly release stored moisture into the soil.

I personally would be very surprised if a mushroom turned up in a Hoya or a Phalaenopsis, but it really depends on the substrate and where you keep them. 

I keep mine in very chunky potting mixes that have very little nutrition (they're epiphytes, so I soak them in nutrient water every so often).

Mushrooms are also less likely to turn up in terracotta pots but since a lot of overwaterers offset their habits by using terracotta pots, don’t take this as gospel.

Nutrients

The lifecycle of leucocoprinus birnbaumii is basically grow mycelium, eat a load of decaying matter, produce a mushroom, release spores, reabsorb mushroom, repeat.

They can’t produce a fruit if they don’t have the nutrients.

The nutrients in your houseplant pot will depend on, er, what’s in the substrate. Some people use compost, which would be good for leucocoprinus birnbaumii, but even better for fungus gnats, which is why I don’t use it.

Some - particularly chain - garden centre pot houseplants up in outdoor potting soil (i.e. a tonne of compost), but add stuff to make it airier. 

I find my houseplants grow perfectly well in it, but it's more likely to yield mushrooms (and fungus gnats). 

I know I said this at the beginning, but a mushroom growing in a houseplant doesn’t automatically make it ‘good soil’.

What it does show is that it’s nutrient-rich, and hasn’t been treated with a tonne of microbe-killing chemicals, which is a good thing.

Does that mean it’s better than pon? No, it’s just different.

Final thoughts

I have an article dedicated to potential problems and benefits that can come from mushrooms growing in houseplants. If I’d gone into detail here it would have been about 10,000 words long.

To summarise, mushrooms are common in houseplant soil because the particular species that we get hails from the tropics and hitchhiked across the globe in botanist’s collections.

They thrive in greenhouses and therefore manage to make their way into millions of houseplants. If you then provide it the right conditions for it to fruit, it’ll grow a mushroom.